Officials said that the twin bombs went off within seconds of each other. The interior ministry said the bombs were hidden with other officials saying the devices had been concealed in a tree between two security posts.

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The moment of the second explosion has been caught on tape.

Egyptian state television said that the double explosions happened outside Cairo University’s engineering facility during clashes between security forces and students. It described the devices as crude and homemade.

Egypt’s security forces have been the target of frequent attacks since a military backed coup toppled President Mohamed Morsi last July. Although attacks have mainly been on the restive Sinai Peninsula, they have begun to spread to major urban areas like Cairo.

Morsi’s supporters have staged regular protests against the military appointed government, which the authorities say have killed almost 500 people, most of them police and soldiers.

Egyptian police brigadier-general TarekEl-merjawy was killed as two blasts hit outside Cairo University on Wednesday, state television said. Four police officers were wounded in an attack on a police vehicle, Reuters reported, citing security officials